1. Field of the Invention
This invention relates to novel aromatic methylidene compounds which are useful as a functional material in electrophotographic photosensitive bodies or as a functional material, such as a charge transport material or a light-emitting material, in organic electroluminescent devices or as a functional material used in other various types of organic semiconductor devices. The invention also relates to intermediate aromatic aldehyde compounds and methylstyryl compounds, both useful for preparing the methylidene compounds, and methods for preparing the intermediate compounds and the methylidene compounds.
2. Description of the Prior Art
Electroluminescent devices that make use of an electroluminescent phenomenon of a substance are self-luminescent in nature, and are thus higher in visuality than liquid crystal devices, ensuring a clear display. Because of the complete solid-state device, they have prominent features of good impact resistance and the like, and are expected as being widely used in the fields of thin displays, back light of liquid crystal displays, plane light sources and the like.
Existing electroluminescent devices are those of a dispersion type which make use of inorganic materials such as zinc sulfide. However, such dispersion-type electroluminescent devices are not in wide use because a relatively high AC voltage is necessary for their drive, with the attendant problem that a drive circuit becomes complicated along with low luminance.
On the other hand, an organic electroluminescent device using organic materials has been proposed by C. W. Tang, for example, in Japanese Laid-open Patent Application No. Hei 63-264692. The device includes a builtup structure of an electron transport organic fluorescent material layer and a hole-transport organic material layer wherein both electron and hole carriers are injected into the fluorescent material layer to permit light emission. It is stated in the application that this electroluminescent device has a much improved luminascent efficiency, and is capable of emission at 1000 cd/m2 or more on application of a voltage of 10V or below. Since the beginning of the above proposal, extensive studies have been made on the related fields of the organic electroluminescent device. At present, various types of materials and device structures have been proposed with extensive studies and developments being directed to practical applications.
Organic electroluminescent devices using materials proposed up to now have, in fact, several problems to solve. Mention is made of some instances of the problems including the lowering of an emission luminance through degradation in function of a device which is only stored irrespective of whether the device is in a driven or non-driven condition, the occurrence of a degradation phenomenon wherein a non-emitting region called dark spot occurs and grows in the course of driving or non-driving, finally resulting in the breakage of the device via short-circuiting.
Such phenomena rely greatly on the fundamental problem of the materials used in the device, and the device may not be satisfactory with respect to the service life thereof. For the service of the device, limitation has to be placed on applications to devices of a type which are responsible only for a relatively short life.
Further, taking the color mode of the device into consideration, systems and light-emitting materials meeting this requirement are not provided satisfactorily at present. In order to solve the above problems and find use in wide fields of organic electroluminescent devices, there has been a strong demand of development of novel materials used in the device such as novel high-performance light-emitting materials, charge transport materials, and the like.
It is therefore an object of the invention to provide novel aromatic methylidene compounds useful as a light-emitting material so as to realize an organic electroluminescent device that can be driven at low voltage, ensures light emission of high luminance and is excellent in durability.
It is another object of the invention to provide novel aromatic aldehyde compounds and methylstyryl compounds, both useful for preparing the above-mentioned novel aromatic methylidene compounds.
It is a further object of the invention to provide methods for preparing the aromatic methylidene compounds.
It is a still further object of the invention to provide methods for preparing the aromatic aldehyde compounds and methylstyryl compounds, respectively.
According to one embodiment of the invention, there is provided a novel aromatic methylidene compound selected from the group consisting of compounds of the following general formulas (1), (1a), (1b), (1c) and (1d): 
wherein R11 and R21 independently in each occurrence represent an unsubstituted or substituted alkyl group, an unsubstituted or substituted alkoxy group, a halogen, e.g. chlorine, bromine, iodine, fluorine, a cyano group or a nitro group, n11 is an integer of 0, 1, 2, 3, 4, 5 or 6, and n21 is an integer of 0, 1, 2, 3 or 4 provided that when n11 and n21 are, respectively, an integer of 2 or more, R11 and R21 may be, respectively, the same or different, and R31 and R41 independently represent hydrogen except the case where both R31 and R41 are hydrogen at the same time, an unsubstituted or substituted alkyl group except the case where both R31 and R41 are an alkyl group at the same time, an unsubstituted or substituted cycloalkyl group except the case where both R31 and R41 are the cycloalkyl group at the same time, an unsubstituted or substituted aromatic group, or an unsubstituted or substituted aromatic heterocyclic group, or may join to complete a condensed ring of unsubstituted or substituted aromatic rings or unsubstituted or substituted aromatic heterocyclic rings; 
wherein R11a, R21a, n11a, n21a, R31a and R41a, respectively, have the same meanings as R11, R21, n11, n21, R31 and R41 defined with respect to the formula (1); 
wherein R11b, R21b, n11b, n21b, R31b and R41b, respectively, have the same meanings as R11, R21, n11, n21, R31 and R41 defined with respect to the formula (1); 
wherein R11c, R21c, n11c, n21c, R31c and R41c, respectively, have the same meanings as R11, R21, n11, n21, R31 and R41 defined with respect to the formula (1), like formulas (1a) and (1c); and 
wherein R11d, R21d, n11d, n21d, R31d and R41d, respectively, have the same meanings as R11, R21, n11, n21, R31 and R41 defined with respect to the formula (1), like formulas (1a) and (1c).
According to another embodiment of the invention, there are also provided intermediate compounds useful for preparing the corresponding aromatic methylidene compounds of the above formulas (1), (1a), (1b), (1c) and (1c). The novel intermediate compounds corresponding to the aromatic methylidene compound (1) are indicated as having the following general formulas (2) and (3): 
wherein R12 and R22, respectively, correspond to R11 and R21 and independently in each occurrence represent an unsubstituted or substituted alkyl group, an unsubstituted or substituted alkoxy group, a halogen, a cyano group or a nitro group, n12 is an integer of 0, 1, 2, 3, 4, 5 or 6, and n22 is an integer of 0, 1, 2, 3 or 4 provided that when n12 and n22 are, respectively, an integer of 2 or more, R12""s and R22""s may be, respectively, the same or different; and 
wherein R13 and R23, respectively, correspond to R12 and R22 and independently in each occurrence represent an unsubstituted or substituted alkyl group, an unsubstituted or substituted alkoxy group, a halogen, a cyano group or a nitro group, n13 is an integer of 0, 1, 2, 3, 4, 5 or 6, and n23 is an integer of 0, 1, 2, 3 or 4 provided that when n13 and n23 are, respectively, an integer of 2 or more, R13""s and R23""s may be, respectively, the same or different.
Likewise, the intermediate compounds corresponding to the aromatic methylidene compound (1a) are indicated by the following general formulas (2a) and (3a): 
wherein R12a and R22a, respectively, correspond to R12 and R22 and independently in each occurrence represent an unsubstituted or substituted alkyl group, an unsubstituted or substituted alkoxy group, a halogen, a cyano group or a nitro group, n12a is an integer of 0, 1, 2, 3, 4, 5 or 6, and n22a is an integer of 0, 1, 2, 3 or 4 provided that when n12a and n22a are, respectively, an integer of 2 or more, R12a""s and R22a""s may be, respectively, the same or different; and 
wherein R13a and R23a, respectively, correspond to R13 and R23 and independently in each occurrence represent an unsubstituted or substituted alkyl group, an unsubstituted or substituted alkoxy group, a halogen, a cyano group or a nitro group, n13a is an integer of 0, 1, 2, 3, 4, 5 or 6, and n23a is an integer of 0, 1, 2, 3 or 4 provided that when n13a and n23a are, respectively, an integer of 2 or more, R13a""s and R23a""s may be, respectively, the same or different.
The intermediate compounds corresponding to the aromatic methylidene compound (1b) are indicated by the following general formulas (2b) and (3b): 
wherein R12b, R22b, n12b and n22b, respectively, have the same meanings as R12, R22 n12 and n22; and 
wherein R13a, R23a, n13b and n23b, respectively, have the same meanings as R13, R23 n13 and n23.
Moreover, the intermediate compounds corresponding to the aromatic methylidene compound (1c) are indicated by the following general formulas (2c) and (3c): 
wherein R12c, R22c, n12c and n22c, respectively, have the same meanings as R12, R22 n12 and n22; and 
wherein R13c, R23c, n13c and n23c, respectively, have the same meanings as R13, R23 n13 and n23.
The intermediate compounds corresponding to the aromatic methylidene compound (1d) are indicated by the following general formulas (2d) and (3d): 
wherein R12d, R22d, n12d and n22d, respectively, have the same meanings as R12, R22 n12 and n22; and 
wherein R13d R23d, n13d and n23d, respectively, have the same meanings as R13, R23, n13 and n23.
The intermediate compounds of the above formulas (2), (2a), (2b), (2c), (2d), (3), (3a), (3b), (3c) and (3d) are useful for preparing the novel methylidene compounds (1), (1a), (1b), (1c), (1d), respectively, as one of starting materials for the methylidene compounds. Other types of compounds may also be used for the preparation of the methylidene compounds. More particularly, the aromatic methylidene compound, for example, of the afore-indicated formula (1) may be prepared broadly through four reaction routes including (I) the reaction between a bismethylphosphonic ester derivative and a styrylbenzaldehyde derivative, (II) the reaction between a bis(4-formylstyryl)naphthalene derivative and a methylphosphonic ester derivative, (III) the reaction between a phthalaldehyde derivative and a methylphosphonic ester derivative, and (IV) the reaction between a bismethylphosphonic ester derivative and a ketone derivative. In addition, the methylidene compound may also be prepared by using, in place of the methylphosphonic ester derivatives in (I) to (IV), corresponding methyltriarylphosphonium salts.
This is true of the preparation of the methylidene compounds of the general formulas (1a), (1b), (1c) and 1(d). Accordingly, the preparation of these compounds is first described with respect to the methylidene compound of the formula (1).
Thus, according to a further embodiment of the invention, there is provided a method for preparing an aromatic methylidene compound of the general formula (1). As described hereinabove, the methylidene compound is obtainable broadly through the four different reaction routes (I) to (IV) set out hereinbelow.
(I) The methylidene compound of the formula (1) is prepared by reaction between a bismethylphosphonic ester derivative of the following formula (4), or a corresponding methyl triarylphosphonium compound thereof wherein the aryl moiety includes, for example, phenyl, tolyl or the like herein and whenever it the term xe2x80x9ccorresponding methyl triarylphosphonium compoundxe2x80x9d appears hereafter and, and a benzaldehyde derivative of the following formula (5); 
wherein R14 represents an unsubstituted or substituted alkyl group, an unsubstituted or substituted alkoxy group, both as defined with respect to R11 in the general formula (1), a halogen group, a cyano group or a nitro group, n14 is an integer of 0, 1, 2, 3, 4, 5 or 6 provided that if n14 is an integer of 2 or over, R14""s may be the same or different, and R represents an unsubstituted or substituted alkyl group; and 
wherein R24 represents an unsubstituted or substituted alkyl group, an unsubstituted or substituted alkoxy group, both as defined with respect to R21 in the general formula (1), a halogen group, a cyano group or a nitro group, n24 is an integer of 0, 1, 2, 3 or 4 provided that if n24 is an integer of 2 or over, R24""s may be the same or different, and R32 and R42, respectively, have the same meanings as R31 and R41 in the formula (1) and independently represent hydrogen except the case where both R32 and R42 are hydrogen at the same time, an unsubstituted or substituted alkyl group except the case where both R32 and R42 are an alkyl group at the same time, an unsubstituted or substituted cycloalkyl group except the case where both R32 and R42 are the cycloalkyl group at the same time, an unsubstituted or substituted aromatic group, or an unsubstituted or substituted aromatic heterocyclic group, or may join to complete a condensed ring of unsubstituted or substituted aromatic rings or unsubstituted or substituted aromatic heterocyclic rings.
(II) The methylidene compound of the formula (1) is also obtained by reaction between a bis(4-formylstyryl)naphthalene derivative of the afore-indicated general formula (2) and a methylphosphonic ester derivative of the following general formula (6) or a corresponding methyl triarylphosphonium compound thereof; 
wherein R33 and R43, respectively, have the same meanings as R31 and R41 in the formula (1), like R32 and R42, and R represents an unsubstituted or substituted alkyl group having from 1 to 4 carbon atoms.
(III) The methylidene compound of the formula (1) is obtained by reaction between a phthalaldehyde derivative of the following general formula (7) and a methylphosphonic ester derivative of the following general formula (8), or a corresponding methyl triarylphosphonium compound thereof: 
wherein R15 has the same meaning as R11 in the formula (1) and n15 has the same meaning as n11 provided that when n15 is 2 or over, R15xe2x80x2s may be the same or different; and 
wherein R25 has the same meaning as R21 in the formula (1), n25 is an integer of 0, 1, 2, 3 or 4 provided that if n25 is 2 or over, R25""s may be the same or different, R34 and R44, respectively, have the same meanings as R31 and R41, like R32 and R42 and the like, and R represents an unsubstituted or substituted alkyl group as defined in the foregoing formulas.
(IV) The methylidene compound of the formula (1) is also obtained by reaction between a bismethylphosphonic ester derivative of the following general formula (9), or a corresponding methyl triarylphosphonium compound thereof, and a ketone derivative of the following general formula (10): 
wherein R16 and R26, respectively, have the same meanings as R11 and R21 in the formula (1) and n16 is an integer of 0, 1, 2, 3, 4, 5, or 6 and n26 is an integer of 0, 1, 2, 3 or 4 provided that if n16 and n26, respectively, are 2 or over, R16""s and R26""s may be the same or different, and R represents an unsubstituted or substituted alkyl group defined in the foregoing formulas; and 
wherein R35 and R45, respectively, have the same meanings as R31 and R41 in the formula (1).
The preparation of other types of methylidene compounds represented by the general formulas (1a), (1b), (1c) and (1d) is likewise feasible using slightly different types of starting materials, and four reaction routes of individual methylidene compounds are depicted below as (Ia) to (IV a) to (Id) to (IV d) wherein like symbols, such as 11, 11a, 11b, 11c, 11d, in the chemical formulas indicate like groups or values and are not defined in the following formulas.
(Ia) The methylidene compound of the formula (1a) is prepared by reaction between a bismethylphosphonic ester derivative of the following formula (4a), or a corresponding methyl triarylphosphonium compound thereof, and a benzaldehyde derivative of the following formula (5a); 
(IIa) The methylidene compound of the formula (1a) is also obtained by reaction between a bis(4-formylstyryl)naphthalene derivative of the afore-indicated general formula (2a) and a methylphosphonic ester derivative of the following general formula (6a) or a corresponding methyl triarylphosphonium compound thereof; 
(IIIa) The methylidene compound of the formula (1a) is obtained by reaction between a phthalaldehyde derivative of the following general formula (7a) and a methylphosphonic ester derivative of the following general formula (8a), or a corresponding methyl triarylphosphonium compound thereof: 
(IV a) The methylidene compound of the formula (1a) is also obtained by reaction between a bismethylphosphonic ester derivative of the following general formula (9a), or a corresponding methyl triarylphosphonium compound thereof, and a ketone derivative of the following general formula (10a): 
(Ib) The methylidene compound of the formula (1b) is prepared by reaction between a bismethylphosphonic ester derivative of the following formula (4b), or a corresponding methyl triarylphosphonium compound thereof, and a benzaldehyde derivative of the following formula (5b); 
(IIb) The methylidene compound of the formula (1b) is also obtained by reaction between a bis(4-formylstyryl)naphthalene derivative of the afore-indicated general formula (2b) and a methylphosphonic ester derivative of the following general formula (6b) or a corresponding methyl triarylphosphonium compound thereof; 
(IIIb) The methylidene compound of the formula (1b) is obtained by reaction between a phthalaldehyde derivative of the following general formula (7b) and a methylphosphonic ester derivative of the following general formula (8b), or a corresponding methyl triarylphosphonium compound thereof: 
(IV b) The methylidene compound of the formula (1b) is obtained by reaction between a bismethylphosphonic ester derivative of the following general formula (9b), or a corresponding methyl triarylphosphonium compound thereof, and a ketone derivative of the following general formula (10b): 
(Ic) The methylidene compound of the formula (1c) is prepared by reaction between a bismethylphosphonic ester derivative of the following formula (4c), or a corresponding methyl triarylphosphonium compound thereof, and a benzaldehyde derivative of the following formula (5c); 
(IIc) The methylidene compound of the formula (1c) is also obtained by reaction between a bis(4-formylstyryl)naphthalene derivative of the afore-indicated general formula (2c) and a methylphosphonic ester derivative of the following general formula (6c) or a corresponding methyl triarylphosphonium compound thereof; 
(IIIc) The methylidene compound of the formula (1c) is obtained by reaction between a phthalaldehyde derivative of the following general formula (7c) and a methylphosphonic ester derivative of the following general formula (8c), or a corresponding methyl triarylphosphonium compound thereof: 
(IV c) The methylidene compound of the formula (1c) is obtained by reaction between a bismethylphosphonic ester derivative of the following general formula (9c), or a corresponding methyl triarylphosphonium compound thereof, and a ketone derivative of the following general formula (10c): 
(Id) The methylidene compound of the formula (1d) is prepared by reaction between a bismethylphosphonic ester derivative of the following formula (4d), or a corresponding methyl triarylphosphonium compound thereof, and a benzaldehyde derivative of the following formula (5d); 
(IId) The methylidene compound of the formula (1d) is also obtained by reaction between a bis(4-formylstyryl)naphthalene derivative of the afore-indicated general formula (2d) and a methylphosphonic ester derivative of the following general formula (6d) or a corresponding methyl triarylphosphonium compound thereof; 
(IIId) The methylidene compound of the formula (1d) is obtained by reaction between a phthalaldehyde derivative of the following general formula (7d) and a methylphosphonic ester derivative of the following general formula (8d), or a corresponding methyl triarylphosphonium compound thereof: 
(IV d) The methylidene compound of the formula (1d) is obtained by reaction between a bismethylphosphonic ester derivative of the following general formula (9d), or a corresponding methyl triarylphosphonium compound thereof, and a ketone derivative of the following general formula (10d): 
Next, the preparation of the intermediate compounds of the afore-indicated formulas (2), (2a), (2b), (2c), (2d), and (3), (3a), (3b), (3c), (3d) are described.
The compound of the general formula (2) is prepared by reaction between the bismethylphosphonic ester derivative of the afore-indicated formula (4), or a corresponding methyl triarylphosphonium compound thereof, and an aldehyde compound of the following general formula (11) 
wherein R27 represents a unsubstituted or substituted alkyl group, an unsubstituted or substituted alkyl group, a halogen atom, a cyano group or a nitro group as defined in R22 in the formula (2), n27 is an integer of 0, 1, 2, 3 or 4 provided that if n27 is 2 or over, R27""s may be the same or different, and R represents an unsubstituted or substituted alkyl group as defined in the foregoing formulas, followed by conversion of the resultant acetal compound into an aldehyde compound.
Likewise, the compounds of the general formulas (2a), (2b), (2c) and (2d) are, respectively, prepared in the same manner as stated above, but using the reaction between each of the bismethylphosphonic ester derivatives of the afore-indicated formula (4a), (4b), (4c) and 4(d) and the compound of the above-indicated compound of the formula (11), followed by conversion of the resultant acetal compounds into corresponding aldehyde compounds.
Further, the compound of the general formula (2) may also be prepared by reaction between the bismethylphosphonic ester derivative of the afore-indicated formula (4), or a corresponding methyl triarylphosphonium compound thereof, and a tolualdehyde compound of the following general formula (12) 
wherein R28 represents a unsubstituted or substituted alkyl group, an unsubstituted or substituted alkyl group, a halogen atom, a cyano group or a nitro group as defined in R27 in the formula (11), and n28 is an integer of 0, 1, 2, 3 or 4 provided that if n28 is 2 or over, R28""s may be the same or different.
In the latter case, no conversion reaction is necessary.
The compounds of the general formulas (2a), (2b), (2c) and (2d) are also prepared in the same manner as mentioned above using the ester derivatives of the afore-indicated general formulas (4a), (4b), (4c) and (4d), respectively.
The compound of the general formula (3) is prepared by reaction between the bismethylphosphonic ester derivative of the afore-indicated formula (4), or a corresponding methyl triarylphosphonium compound thereof, and an aldehyde compound of the following general formula (13): 
wherein R29 represents an unsubstituted or substituted alkyl group, an unsubstituted or substituted alkoxy group, a halogen atom, a cyano group or a nitro group as defined as R14 in the formula (4), and n29 is an integer of 0, 1, 2, 3 or 4 provided that if n29 is 2 or over, R29xe2x80x2s may be the same or different.
The compounds of the general formulas (3a), (3b), (3c) and (3c) can be, respectively, prepared in the same manner as stated above but using, in place of the compound of the general formula (4), the compounds of the afore-indicated general formulas (4a), 4(b), 4(c) and 4(d), respectively.
Moreover, the compound of the general formula (3) may also be prepared by reaction between the aromatic aldehyde compound of the afore-indicated formula (7) and a methylphosphonic ester derivative of the following general formula (14) or a corresponding methyl triarylphosphonium compound thereof: 
wherein R20 represents an unsubstituted or substituted alkyl group, an unsubstituted or substituted alkoxy group, a halogen atom, a cyano group or a nitro group as defined as R23 in the afore-indicated formula (3), n20 is an integer of 0, 1, 2, 3 or 4 provided that if n20 is 2 or over, R20""s may be the same or different, and R represents an unsubstituted or substituted alkyl group having from 1 to 4 carbon atoms.
Likewise, the compounds of the afore-indicated general formulas (3a), (3b), (3c) and (3d) can be prepared in the same manner as set our above but using the compounds of the afore-indicated formulas (7a), (7b), (7c) and (7d) in place of the compound of the formula (7).